A commentary on the growth of the human brain and skull.

This paper tests the suggestion put forth by Tanner (' 5 5) and Eichorn and Bayley ('62) to the effect that the brain participates i n the parapubertal spurt of growth which characterizes many of the dimensions of the human body. To this end, longitudinal data consisting of oriented head roentgenograms of 11 boys were examined. Two measurements were taken directly from each lateral head film: (1) skull length, measured from glabella to opisthocranion, and (2) endocranial length, the maximum length of the endocranial contour in the mid-sagittal plane. While many of the individual cumulative curves depicting growth in skull length exhibit a parapubertal acceleration, all oP the curves for endocranial length comprise segments of a parabolic arc representing a single decelerating phase of growth. Mean incremental curves, mathematically fitted, further emphasize the differences in velocity and pattern of size attainment €or the two dimensions tested. The data here presented, then, fail to implicate the brain in the general spurt of growth evident for the external dimensions of the head a t adolescence. It is suggested that two discrete systems are evident in the growth of the skull: a rapidly growing neural system essentially completed by adolescence, and a facial system of slower growth and longer duration. The conventional measurement of skull length cuts across both systems, appraising neural growth and the cerebral skeletal envelope prior to adolescence, and then superimposing the facial component, the forward projection of the frontal sinus, during adolescence and post-adolescence. Since the publication of Scammon's ('30) curves of differential tissue growth (fig. l) , it has been generally accepted that the curve of brain growth does not exhibit the parapubertal acceleration which characterizes many of the dimensions of the human body. Scammon was of the opinion that the external dimensions of the head also adhered to the " neural " pattern of growth; nevertheless, subsequent studies by Goldstein ('36, '39), Shuttle-worth ('39), Nanda ('55), Dokladal ('59), Eichorn and Bayley ('62), and Miklashev-skaya ('66), among others, have demonstrated the presence of an adolescent spurt in head growth in American and European populations. Thus the dichotomy, equating the brain with the neural mode of growth and the external dimensions of the head with the somatic pattern, became established and reinforced. Recently, however, Tanner ('55) and Eichorn and Bayley ('62) have challenged the conclusion that the brain does not participate in the adolescent acceleration. These authors have analyzed …